300Tdi coolant issue

Evening all.

I’m having some problems with my 300Tdi. Following a head gasket failure a couple of months ago, I had the head skimmed and I put it back together with an Elring gasket.

The car is running fine with decent power and not using coolant. The heater is working and no coolant is being lost.

Problem is, the coolant level in the header tank is rising from the fill level to virtually the top of the tank when the car is driven for 30 mins or more. Temp gauge is fine, sits around the centre of the gauge.

If I release the bleed bungs in the thermostat housing and the radiator, the coolant level is about 50mm below the top. When I release the air, the coolant flows back from the header tank to the rad and thermostat housing.

I’ve changed the thermostat and it made no difference. I’ve put a sniffer test on the header thank and there was no colour change in the indicator fluid.

Any suggestions how the air is getting into the system and why it isn’t bleeding out through the pipes back to the header tank?

Many thanks.

Have a search for vbbleeding coolant system 300tdi.

In a nut shell remove stat bung, fill header tank until level in tank reaches the level mark, refit tank cap and fill rest of system through stat bung, reift stat bung and try again, if still the same I would hazartd a guess you have head gasket failure, not unknown of 300 models.

thanks for that, Lynall.

I’ve bled the coolant via the radiator and thermostat housing as you describe. It all seems fine at idle when hot or cold, but air builds up in the system following a drive.